Publication Date:
2017-04-04
Description:
We conducted initial palaeomagnetic studies on cores from site AND-2A (77°45.488’S,
165°16.605’E, ~383.57 metres water depth). A total of 813 samples were collected that span from the
top of the section down to the base at 1138.54 metres below sea floor (mbsf). Samples were collected
every one or two metres down the core, with paired (pilot) samples being collected about every ten to
twenty metres to allow us to assess the demagnetisation behaviour of the samples using either alternating
field (AF) or thermal demagnetisation. With the exception of only a few intervals, AF demagnetisation
was observed to resolve a characteristic remanent magnetisation (ChRM) as well or better than thermal
demagnetisation. Thermal demagnetisation was particularly ineffective in many intervals owing to thermal
alteration that was common above 500°C and was evident in some samples even at low temperatures.
Above Lithostratigraphic Unit (LSU) 8 (436.18 mbsf), where lithologies are generally more coarse grained
than lower in the section, resolving a ChRM is difficult and recent overprints or a drilling overprint are a
concern. Within LSU 8 and below, most samples have a ChRM that can be resolved. The ChRM is most
likely an original depositional magnetisation throughout most of this lower section, although orthogonal
demagnetisation diagrams contain evidence that normal polarity overprinting affects some intervals. Based on
40Ar/39Ar dates and diatom datums, the magnetozones identified from the base of the hole up to ~266mbsf
are consistent with spanning from either Chron C6n (18.748-19.772 Ma) or C6An.1n (20.040-20.213 Ma)
up through Chron C5Br (15.160-15.974 Ma). Above this, intervals of constant polarity are isolated within
longer stratigraphic intervals of uncertain polarity, making their correlation with the geomagnetic polarity
timescale (GPTS) speculative and highly dependent on ages obtained from other dating methods. One
exception is a reversed-to-normal polarity transition that occurs at ~31 mbsf and is interpreted to most
likely be the Brunhes/Matuyama boundary. The spacing of polarity reversals below 266 mbsf and their
correlation with the GPTS indicates that this part of the stratigraphic section was deposited between 15
to 20 Ma at a mean sedimentation rate of about 18 centimetres (cm)/ thousand year (k.y.).
Description:
Published
Description:
193-210
Description:
2.2. Laboratorio di paleomagnetismo
Description:
N/A or not JCR
Description:
reserved
Keywords:
Magnetostratigraphy
;
ANDRILL
;
Antarctica
;
Paleomagnetism
;
04. Solid Earth::04.04. Geology::04.04.10. Stratigraphy
;
04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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